1. Field of the Invention
The present invention relates to an apparatus for monitoring the degree of mental tension experienced by a person which is used to check the severity of mental tension or to allow a person to train himself to promptly control the degree of tension he experiences during such pursuits as sports, giving lectures, taking examinations and so on, in which person's performance is greatly influenced by the level of mental tension.
2. Related Background Art
Hitherto, many apparatuses which are adapted to monitor the heartbeat (instantaneous heartbeat or mean heartbeat over a predetermined period of time) are designed to measure a load caused by motion. One type of apparatus that is adapted to evaluate and train the automatic nerve function is known as a heartbeat bio feedback and was disclosed in JP-B-61-43056. FIG. 1 shows a schematic block diagram of such an apparatus. In the diagram, reference numeral 1 denotes a pulse wave detecting unit; 2 indicates an amplifier; 3 a heartbeat (sphygmus, pulse) counter; 4 a display circuit; 5 a variable frequency oscillator; 6 a counter; 7 a comparator; and 8 a display circuit.
The pulse wave detected by the detecting unit 1 is amplified by the amplifier 2. The pulse waves are counted by the counter 3 over a predetermined period of time and then the count value is displayed by the display circuit 4. On the other hand, pulses corresponding to the objective heart rate are generated by the variable frequency oscillator 5. The same number of pulses as the count value incremented on the counter 3 are counted over a predetermined period of time by the counter 6. The objective heart rate and the actual pulse frequency, which is output from the counter 3, are compared by the comparator 7. The result of this comparison is then displayed by the display 8.
On the other hand, an RRV (RR interval fluctuation) monitoring apparatus has been developed to evaluate mental loads experienced in conducting computer-related work and the like (refer to an excerpt from the 2nd Symposium on "Human Interface", pages 119 to 122, 1986). As shown in FIG. 2, the monitoring apparatus comprises sensors 11, an amplifier 12, a microcomputer 13 and a display unit 14. FIG. 3 shows an electrocardiogram. In the diagram, P, Q, R, S and T represent P wave, Q wave, R wave, S wave and T wave, respectively, and RRI (R-R Interval) indicates the time interval between two R waves. In the apparatus shown in FIG. 2, the electrocardiogram can be obtained through the sensors 11 and the amplifier 12. Next, in the microcomputer section 13, the R wave in the electrocardiogram is detected to obtain the RRI which is then converted into the interval data at regular intervals. Then a variance (corresponding to the square of the standard deviation SD) is calculated and displayed by the display unit 14. Another known example of such an apparatus is the apparatus for measuring the respiratory circulating function disclosed in JP-A-61-272034.
Since only the heart rate is displayed in the conventional heart rate monitor, there is a problem in that any physiological change in the heartbeat due to changes in motion, posture, respiration pattern and the like cannot be differentiated mental tension; hence any change in mental tension degree cannot be accurately monitored. On the other hand, the RRV monitor also has a similar problem because all of the fluctuation components are lumped together to be evaluated.